My grandfather, Charles Wilson, was a milkman. He first delivered milk by horse and buggy and then moved on to truck delivery. In the 1930 and 1940 censuses, he was listed as a truck driver for a creamery company. On his Social Security application from 1939, he listed his employer as Ebling Creamery.
The picture below shows Papa receiving an award of some sort from Sealtest in the 1960s or 1970s, perhaps for his retirement.